Holographic disc recording system

Abstract

A holographic disc recording system for recording, in the form of holograms, information stored on a source disc onto a target disc includes a conical beam shaper which transforms a reference beam into a conical beam having a substantially cylindrically symmetrical shape and including light rays which travel along lines which intersect a beam axis of the conical beam at substantially the same angle with respect to the beam axis. The conical beam is incident on the target disc while the beam axis of the conical beam substantially coincides with a central axis of the target disc, so that substantially all of the light rays of the conical beam are incident on the target disc at substantially the same angle.

1. A holographic disc recording system for recording, in the form of holograms, information stored on a transmissive source disc onto a target disc composed of a holographic recording material, the holographic disc recording system comprising:
 a beam generator which generates a plane-wave beam of collimated coherent light; 
 a beam splitter which splits the beam emitted by the beam generator into a first beam used as a signal beam and a second beam used as a reference beam; 
 an optical unit which guides the first beam such that the first beam passes through the source disc and is incident on the target disc at one side thereof and guides the second beam such that the second beam is incident on the target disc at the other side thereof without passing through the source disc; 
 a plurality of conical beam shapers for emitting conical beams which are incident on the target disc at different angles; and 
 a conical beam shaper selecting mechanism for selectively using one of the conical beam shapers, 
 wherein the optical unit includes the one of the conical beam shapers, and the one of the conical beam shapers transforms the second beam into a conical beam having a substantially cylindrically symmetrical shape and including light rays which travel along lines which intersect a beam axis of the conical beam at substantially the same angle with respect to the beam axis, and 
 wherein the optical unit is constructed such that the beam axis of the conical beam incident on the target disc substantially coincides with a central axis of the target disc, so that substantially all of the light rays of the conical beam are incident on the target disc at substantially the same angle. 
 
     
     
       2. A holographic disc recording system according to  claim 1 , wherein the optical unit includes beam-diameter increasing means, and wherein the first beam covers the entire recording area of the source disc when the first beam passes through the source disc and is incident on substantially the entire effective recording area of the target disc, and the second beam is incident on substantially the entire effective recording area of the target disc. 
     
     
       3. A holographic disc recording system according to  claim 1 , wherein at least one of the conical beam shapers is a conical mirror. 
     
     
       4. A holographic disc recording system according to  claim 1 , wherein at least one of the conical beam shapers is a conical prism. 
     
     
       5. A holographic disc recording system according to  claim 1 , wherein at least one of the conical beam shapers is an inverted conical prism. 
     
     
       6. A holographic disc recording system according to  claim 1 , further comprising a polarizer which polarizes at least one of the first beam and the second beam such that the beam is polarized in the radial direction of the target disc when the beam is incident on the target disc. 
     
     
       7. A holographic disc recording system according to  claim 1 , further comprising an attenuator which attenuates at least one of the first beam and the second beam to make the light intensity uniform, so that the beam has substantially uniform light intensity over substantially the entire effective recording area of the target disc when the beam is incident on the target disc.